The gasification of biomass, such as woody biomass, in a pyrolysis gasification system and conversion of the biomass, which has been conventionally treated as waste, into resources for effective use has been in demand. Biomass, compared to fossil fuels and the like, is low in energy density. One known method for increasing the energy density of biomass is a torrefied method in which most of a heat quantity in a woody biomass is caused to remain, and a fiber portion (cellulose and lignin) contained in the woody biomass is thermally decomposed (refer to Patent Document 1, for example).
The semi-carbonization method is a technique in which a torrefied material (torrefied fuel) is produced by pyrolyzing woody biomass at 250° C. to 350° C. in the absence of oxygen. With the decomposition of the fiber portion, the torrefied material becomes easy to pulverize, making it possible to pulverize the material using a pulverizer (mill) and then use the material as fuel for a pulverized coal boiler.
Herein, a conventional coal-fired thermal power generation system will be described with reference to FIG. 2. A coal-fired thermal power generation system 101 utilizes a torrefied material T manufactured by pyrolyzing a woody biomass B in a pyrolysis gasification furnace 4 as fuel in a coal-fired power plant 7.
Specifically, the torrefied material T is pulverized by a pulverizer 15 along with a coal C supplied from a coal bunker 14, and introduced as a pulverized coal PC into a pulverized coal boiler 16. Then, steam produced by the heat produced when the pulverized coal PC was caused to combust in the pulverized coal boiler 16 is introduced into a steam turbine 17, and power is generated in a power generator 18 directly connected to the steam turbine 17.
In this coal-fired thermal power generation system 101, a pyrolysis gas P produced in the pyrolysis gasification furnace 4 and separated in a cyclone 6 is caused to combust in a combustion furnace 3. A combustion exhaust gas E produced by this combustion is utilized as a heat source for the pyrolysis gasification furnace 4 itself, thereby decreasing the use of an auxiliary fuel F, the auxiliary fuel F being the fuel of the combustion furnace 3. Moreover, the cyclone 6 can also be omitted.